E3L5: Cell Cycle I

Question 1

What is NOT one of the three types of cyclin present in the cell cycle?

A. G1/S-Cyclin

B. G2/S-Cyclin

C. S-Cyclin

D. M-Cyclin

Answer 1

B. G2/S-Cyclin does not exist.

Question 2

Which of the following can effectively inhibit Cdk? Circle all that apply.

A. Wee1 Kinase

B. Cdc25 phosphotase

C. P21

D. CAK

Answer 2

A. Wee1 Kinase

C. P21 (Cdk inhibitor protein)

Question 3

Which of the following enzymes acts as an oncogene in almost 30% of breast cancers?

A. Wee1 Kinase

B. Cdc25 phosphatase

C. CAK

D. SCF

Answer 3

B. Cdc25 phosphatase

Question 4

Which of the following are ubiquitin ligases? Circle all that apply.

A. SCF

B. APC

C. p53

D. waf1

Answer 4

A. SCF: degrades G1/S-cyclins

B. APC: degrades M-cyclins

Question 5

*Critical thinking*

What happens if you knock out SCF?

A. M-phase will be prolonged

B. S-phase will be prolonged

C. M-phase will be shortened

D. S-phase will be shortened

Answer 5

B. S-phase will be prolonged

SCF is a ubiquitin ligase that degrades G1/S-cyclins. If you KO SCF, then G1/S-Cdk remains ACTIVE.

Question 6

*Critical thinking*

What happens if you knock out APC?

A. M-phase is prolonged

B. S-phase is prolonged

C. M-phase is shortened

D. S-phase is shortened

Answer 6

A. M-phase is prolonged

Note: if chromosomes are unnattached to spindle in mitosis, APC will not break down M-cyclin.

Question 7

Rb is active at what phase of mitosis?

A. M

B. G1

C. S

D. G2

Answer 7

B. G1 phase

Question 8

What does Rb bind and sequester?

A. E2F

B. EF2

C. G1-Cdk

D. S-Cdk

Answer 8

A. E2F

Question 9

Which of the following is NOT the role of E2F?

A. Promotes S-phase gene transcription

B. Promotes S-cyclin transcription

C. Eukaryotic initiation factor

D. Is released from Rb sequestration, by viral proteins

Answer 9

C. Eukaryotic initiation factor

Question 11

DNA damage has which of the following effects?

A. Phosphorylation of Mdm2, thus releasing p53

B. Phosphorylation of p53, thus releasing Mdm2

C. Transcription of the p53 gene by p53

D. p53 degradation by proteosomes

Answer 11

B. Phosphorylation of p53, thus releasing Mdm2

Question 12

Which of the following is TRUE about p53?

A. It is a TF for the Waf2 gene

B. It promotes the transcription of p21, a cyclin kinase activator

C. It is an oncogene

D. It is a tumor suppressor

Answer 12

D. It is a tumor suppressor